"The frog from hell" - a giant fossil found in Madagascar - has opened a rift among researchers over when an ancient land bridge closed. The finding supports the controversial view that South America and Madagascar were linked until 80 million years ago - far more recently than previously thought.

The frog, dubbed Beelzebufo, resembles the family of horned toads that are now unique to South America. But, at more than 40 centimetres in length, it would have been more than twice the size of its nearest living relative.

Team member Susan Evans of University College London says the fossil casts doubt on traditional models, which suggest the land connection between South America and Madagascar was lost 120 million years ago. Instead, says Evans, the discovery lends weight to a paleobiogeographical model suggesting that Madagascar, the Indian subcontinent and South America were all linked well into the Late Cretaceous - the age of the dinosaurs.

Primitive Pac-man

Beelzebufo would have weighed around four kilograms with a squat body and a huge head. These features are characteristic of horned toads of the ceratophryine family, also known as "Pac-man frogs" because of their large mouths.

Evans says that the frog would have been the size of a slightly squashed beach-ball. "If it shared the aggressive temperament and 'sit-and-wait' ambush tactics of living horned toads, it would have been a formidable predator," she says, adding that Beelzebufo might even have munched on hatchling or juvenile dinosaurs.

Journal reference: Proceedings of the National Academy of Sciences (DOI: 10.1073/pnas.0707599105).